WYOMING, Mich. (AP) — A pregnant Michigan teenager was strangled and her boyfriend was decapitated after apparently connecting with a stranger through the online service Craigslist for a sexual encounter, police said Monday.

The police chief in Wyoming, a Grand Rapids suburb, said that 18-year-old Brooke Slocum was held captive before her death. Her body was found Thursday in the trunk of the suspect’s car. She was eight months pregnant.

Chief James Carmody says her boyfriend, Charles Oppenneer, 25, was found decapitated in a park a day earlier. His head hasn’t been found.

It’s likely that Oppenneer died of some kind of head trauma, but that couldn’t be determined without his head being found, police said.

Emails indicate that Slocum connected with the suspect, 31-year-old Brady Oestrike, through a Craigslist ad and arranged a sexual encounter where Oppenneer would be present, according to investigators.

Police got a search warrant for Oestrike’s home, and he fled. He fatally shot himself after crashing his car, after which police found Slocum’s body.

Carmody said it has been a “hellish environment” for officers as they investigated the various crime scenes, including Oestrike’s home.

Investigators collected at least 400 items from Oestrike’s home, including firearms, ammunition and knives. They also seized a number of electronics items and possessions from both victims.

Police said they plan to keep investigating to see if there were any other people involved in the killings.